[P4-dev] Cut-through switching specification at P4 level

Saulo Queiroz ssaulojorge at gmail.com
Thu May 18 12:33:33 EDT 2017


If i'm not wrong, some targets offer the feature as an administrative
configuration parameter, i.e.
store-and-forward, cut-through or "dynamic" (following some heuristic to
determine the forwarding mode
in a per frame basis). Unless cut-through is definetly left-behind, would
not be the case to offer such option at
P4 level to be even more platform-generic?

Also, some researchers may test specific algorithms based on the options.



2017-05-17 19:59 GMT-03:00 Andy Fingerhut <andy.fingerhut at gmail.com>:

> I am not aware of any way to specify this in the P4 language (and I've
> read through the spec several times in the last couple of weeks).  The most
> the spec has to say about it is to note that if you want to access a packet
> length field, that would be impossible on a cut-through target
> implementation, so a program accessing such information would not be
> portable to such a target (Section 11.8 "Data Extraction" of the P4-16
> spec).
>
> Just about everything I can think of that you would want to write a P4
> program would be independent of whether the target was cut-through or
> store-and-forward.  Do you have some application or feature in mind where
> that would make a difference to you when writing P4 code?
>
> Andy
>
>
> On Wed, May 17, 2017 at 5:36 AM, Saulo Queiroz <ssaulojorge at gmail.com>
> wrote:
>
>> Hi all,
>>
>> Is it possible to specify at P4 level whether a given target operate
>> as cut-though or store-and-forward?
>>
>> BTW, does switch.p4 support cut-through?
>>
>>
>> thanks in advance
>>
>> --
>> Saulo Jorge bq
>> - "Beware of bugs in the above code; I have only proved it correct, not
>> tried it."
>> Donald Knuth.
>>
>> _______________________________________________
>> P4-dev mailing list
>> P4-dev at lists.p4.org
>> http://lists.p4.org/mailman/listinfo/p4-dev_lists.p4.org
>>
>
>


-- 
Saulo Jorge bq
- "Beware of bugs in the above code; I have only proved it correct, not
tried it."
Donald Knuth.
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